There are a variety of lighting applications that require continuous operation. For example, facilities that are open and in use continuously day and night, such as airports, hospitals, and public attractions are often continuously lit. Light Emitting Diodes (“LEDs”) have become strong candidates for such continuous lighting applications, because they have the longest published life of available light sources. LEDs have unique advantages over other lighting solutions. For example, they operate at a high efficiency to produce more light output with lower input power, and have an inherently longer service life.
Unlike incandescent bulbs and fluorescent lights, LEDs are semiconductor devices that conventionally must operate at lower temperatures. LEDs typically remove heat by conduction from the LED p-n junction to the case of the LED package before being dissipated. Conventional LED packages typically employ various heat removal schemes. The effectiveness of the heat removal scheme determines how well such LEDs perform, as cooler running temperatures yield higher efficacy for a given level of light output, and longer overall lifetime.
One conventional passive approach to cooling LEDs in continuous lighting applications provides a finned heat sink exposed to external air. In such an approach, the thermal choke point in the heat transfer equation is typically the heat sink to air interface. To maximize heat transfer across this interface, the exposed heat sink surface area is typically maximized, and the heat sink fins are typically oriented to take advantage of any existing air flow over the fins. Unfortunately, such a conventional passive approach does not effectively cool LEDs for various reasons. Thus, in typical LED lighting applications that utilize this approach, the LEDs are often operated at less than half of their available light output capacity, to extend their lifetime and to preserve their efficiency.
Other LED continuous lighting applications utilize a conventional active approach to cooling LEDs that forces air over a finned heat sink with, for example, a powered fan. Another example is a patent pending product, referred to as “SynJet,” which uses a diaphragm displacement method to “puff” air over a finned heat sink. While such active approaches may be more effective in removing heat from LEDs than many passive approaches, they have many negative issues. The issues with these active cooling techniques include noise, cost, size, and that the active components may not last as long as the LEDs.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent upon a reading of the specification and a study of the drawings.